You only get paid from Amazon if someone that live in the country you Have signed up your Amazon account click and buy from your Amazon Affiliate link. So if you have a UK Amazon account you only get paid From the people that lives in the UK, and you don't get paid anything from Amazon if a person from US buy throughout your Amazon affiliate link. You are missing out on huge revenue opportunities.
Dom W. Has Written a great instruction article on how to how to using the Amazon Link localizer that solve the problem. This instruction I have written Shows the process of how to sign up for Affilliate accounts in several Countries. Before proceeding any further read Dom W's, Instruction, How to using the Amazon Link Localizer.
Part 1.
I Assume that you have signed up for an Amazone Affiliate account, and You have reached this screen shot. Move your mouse to the upper right on the screen, and press the country you want to get a new affiliate account.